The present invention relates to wireless cellular telecommunication systems. More particularly, and not by way of limitation, the invention is directed to a system and method for mitigating inter-cell interference through coherent, coordinated multipoint transmission and reception.
Inter-cell interference in a wireless cellular telecommunication network is one of the most dominant sources for performance impairment. Traditional approaches to mitigating this impairment include measures such as frequency reuse and spread spectrum. More recently, Inter-Cell Interference Coordination (ICIC) solutions that rely on the ad hoc coordination of multiple cells have also been proposed. See, for example, the Ericsson Contribution, “On Inter-cell Interference Coordination Schemes without/with Traffic Load Indication,” 3GPP TSG-RAN WG1 R1-072456.
One solution to mitigate the inter-cell interference is to connect multiple cells to a central controller unit, which coordinates the transmission and reception to and from the User Equipments (UEs) so that interference can be avoided by scheduling, or can be actively suppressed using signal processing techniques. This type of solution may be referred to as Coordinated Multi-Point (CoMP) transmission and reception. In this context, a “CoMP cell” is a collection of geographically contiguous cells, referred to as sub-cells, connected to the same central unit. Signal processing techniques that actively cancel or suppress interference are sometimes referred to as coherent CoMP techniques. One such signal processing technique, referred to as Zero Forcing, has been shown to achieve significant gain. More details regarding CoMP and Zero Forcing may be gained from “Network Coordination for Spectrally Efficient Communications in Cellular Systems,” by Karakayali, Foschini, and Valenzuela.
A drawback of utilizing a signal processing technique such as Zero Forcing is that the instantaneous Multiple-input Multiple-Output (MIMO) channels between all the UEs and cells must be communicated to the central agent. This can only be achieved by installing a high capacity back haul channel. Additionally, the performance of such ad hoc approaches may not be sufficient to meet future requirements.
FIG. 1 is an illustrative drawing of three adjacent CoMP cells A, B, and C, each comprising a number of sub-cells. In a CoMP architecture, the interference between sub-cells is only coordinated or suppressed within each CoMP cell. In the context of CoMP, this type of interference between sub-cells in a single CoMP cell is referred to as intra-CoMP-cell interference. However, there is no coordination between the larger CoMP cells, and thus the border sub-cells, indicated by shading, may experience interference from transmissions in the border sub-cells of neighboring CoMP cells. The interference among multiple CoMP cells along the shaded border areas shown in FIG. 1 is referred to as inter-CoMP-cell interference. This type of interference still remains a major source of performance impairment.